This invention relates to the preparation of N-phosphonomethylglycine or its derivatives and, more particularly, to an improved process for producing N-phosphonomethylglycine by oxidation of certain .alpha.-alkyl-substituted phosphonomethyliminodiacetic acid intermediates.
N-phosphonomethylglycine, known in the agricultural chemical art as glyphosate, is a highly effective and commercially important phytotoxicant useful in controlling the growth of germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants. Glyphosate, and various inorganic and amine salts thereof, is conveniently applied in the form of an aqueous solution as a post-emergent phytotoxicant or herbicide for the selective control of one or more monocotyledonous species and one or more dicotyledonous species in the presence of other monocotyledons and dicotyledons. Moreover, such compounds are characterized by broad spectrum activity, i.e., they control the growth of a wide variety of plants, including but not limited to ferns, conifers, aquatic monocotyledons, and dicotyledons.
Hershman U.S. Pat. No. 3,969,398 describes a commercially suitable process for the manufacture of glyphosate in which iminodiacetic acid is reacted with formaldehyde and phosphorous acid to produce the intermediate N-phosphonomethyliminodiacetic acid, which is then oxidized for cleavage of one of the acetic acid substituents to produce glyphosate, release carbon dioxide and produce formaldehyde as a by-product.
Parry et al U.S. Pat. No. 3,956,370 describes a process for preparing N-phosphonomethylglycine in which N-benzylglycine is reacted with formaldehyde and phosphorous acid in an acidic aqueous medium to give N-benzyl-N-phosphonomethylglycine. Thereafter the N-benzyl group is cleaved by reaction with hydrobromic or hydroiodic acid to produce glyphosate.
Gaertner U.S. Pat. No. 3,927,080 describes the production of glyphosate by acid hydrolysis of N-t-butyl-N-phosphonomethylglycine or its esters. Tertiary butyl amine is reacted with a bromoacetate ester to produce an ester of N-t-butylglycine, which is in turn reacted with formaldehyde and phosphorous acid to produce the N-t-butyl-N-phosphonomethylglycine precursor.